Shape tailored Ni3(NO3)2(OH)4 nano-flakes simulating 3-D bouquet-like structures for supercapacitors: exploring the effect of electrolytes on stability and performance

Abstract

The present study demonstrates a novel, low temperature synthetic approach by which 3-D bouquets of nickel hydroxide nitrate were processed into high surface area electrodes for supercapacitor applications. The synthesized micro-bouquets comprised randomly arrayed microporous nanoflakes (pore size: 2–6 nm) and exhibited a surface area of 150 m² g⁻¹. Morphological evolution studies were performed to elucidate how surface morphology of these electrode materials affect redox reactions and their ultimate performance as a supercapacitor. The electrodes were tested in three different electrolytes, namely lithium hydroxide, potassium hydroxide and sodium hydroxide. From the detailed electrochemical analysis, an intrinsic correlation between the capacitance, internal resistance and the surface morphology was deduced and explained on the basis of relative contributions from the faradaic properties in different electrolytes. Depending on the surface morphology and electrolyte incorporated, these nano/micro-hybrid electrodes exhibited specific mass capacitance value of as high as 1380 ± 38 F g⁻¹. Inductively coupled plasma-atomic emission spectroscopy was used to determine the electrode dissolution in the given electrolyte and the findings were co-related with the cycling stability. By employing this low cost electrode design, high stability (>5000 cycles with no fading) was achieved in lithium hydroxide electrolyte. Furthermore, a working model supercapacitor in a coin cell form is also shown to exhibit peak power and energy density of 3 kW kg⁻¹ and 800 mW h kg⁻¹, respectively.